This invention relates to a structure which in use is subject to fluid flow. More particularly but not exclusively the invention relates to an aerofoil device especially of an aircraft, such as a rotor blade of a rotary wing aircraft such as a helicopter, or a wing of a non-rotary wing aircraft.
However the invention has application to other aerofoil devices, such as for examples only, propellers and turbine blades, and yet more generally to any device which in use is subject to fluid flow and there is a requirement to vary the geometry of at least a part of the device in use, to affect fluid flow.
Rotor blades for example, have a main body with an outer surface including an upper camber surface and a lower camber surface, and a leading edge and a trailing edge, a blade tip and a root end. The trailing edge particularly of the blade may have attached to it, a control surface, such as for example only, a flap, the position of which is variable to affect fluid flow over the device, for example to improve the performance of the blade, during the transition between hover and forward flight. For example the flap may be lowered from its usual raised position when the helicopter is in forward flight, to a lowered position to improve performance in hover.